Amplifiers used in applications such as pulse-width modulation (PWM) motor drive applications typically include characteristics such as precision, low noise, low offset, fast transient response and settling time, wide common-mode range, high common-mode rejection of both direct current (DC) and alternating current (AC) common-mode signals, and a minimal output glitch response to very fast and large common-mode signal steps. An example amplifier with such characteristics is a chopped amplifier (or chopper amplifier), which is a type of amplifier that typically reduces offset errors by using chopping techniques. Chopped amplifiers convert offset errors into an output ripple at the chopping frequency.
Conventionally, the output ripple is reduced using a ripple filter that is placed inline in the signal path of the chopped amplifier. Inline ripple filters typically reduce the speed of the chopped amplifier significantly because they act as a low pass filter to the signals processed by the chopped amplifier. To improve the speed of chopped amplifiers with inline ripple filters, a feed-forward path can be used to provide a high-frequency bypass signal path for the chopped amplifier. A drawback with adding the feed-forward path is an increased input capacitance that reduces the AC common-mode rejection ratio and also increases output glitches in response to common-mode transients.
Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follows.